1. Field of the Invention
The present invention relates to an article to be processed having identification (ID) and a method of producing the article.
2. Related Background Art
Attaching an ID to an article to be processed is widely adopted for the production management thereof.
For example, solar cell modules are produced principally in 6 V type and 12 V type, and the assembly of photovoltaic elements and the systemization by linking with a battery or with an inverter have to be executed corresponding to such output type. Also a solar cell module integral with a roofing material has been actively developed for use in ordinary houses, and various products in size and color have to be manufactured because the design of the roof is considered important. For this reason, there are required various photovoltaic elements different in size and in output, and the manufacturing process is managed by providing each photovoltaic element with an ID.
On the other hand, for mass producing the photovoltaic elements of various sizes, there are required mass production lines corresponding to such sizes. If these elements are to be produced in a line, the productivity will be deteriorated since a change or an adjustment in the conveying mechanism and the aligning mechanism for the supply of each component is required for each type of the elements. Also the tact time of the mass production line is limited and becomes the same for a photovoltaic element of a large size and that of a small size, and the production efficiency in terms of the produced area becomes deteriorated. Therefore, the productivity inevitably becomes low and the production cost becomes high if the photovoltaic elements of various sizes are to be manufactured by such method.
On the other hand, Japanese Patent Application Laid-Open No. 7-321354 discloses a method of producing the photovoltaic elements of various sizes on a single production line with a high productivity. It also discloses a method of mass producing the photovoltaic element of a large size and then dividing it by cutting according to the requirement, thereby providing the solar cell module of a low cost, without the necessity of originally producing the photovoltaic cell of each size. Also in such case, the production is managed by attaching ID to each unit of the photovoltaic element of a large size, which is the processing unit in the mass production.
FIGS. 1A to 1D show an example of the above-mentioned photovoltaic element provided with an ID, wherein FIG. 1A is a plan view thereof, FIG. 1B is a cross-sectional view along the line 1B—1B of FIG. 1A, FIG. 1C is a cross-sectional view along the line 1C—1C of FIG. 1A, and FIG. 1D is a bottom plan view thereof. A current-collecting electrode 102 formed on a semiconductor substrate 101 has a function of efficiently collecting the electric current generated in the semiconductor substrate 101. The current-collecting electrode 102 is formed by adhering with a carbon paste a copper wire, which is of a low cost and has a low resistance loss, to the element. A positive electrode lead terminal 103 has a function of collecting the current from the current-collecting electrode 102 and guiding the current to the exterior. It is composed of a silver-clad copper foil. The silver-clad copper foil is employed in order to reduce a contact resistance between the positive electrode lead terminal 103 and the current-collecting electrode 102 because of use of silver. The positive electrode lead terminal 103 is adhered onto a double-faced insulating adhesive tape 104 provided on the semiconductor substrate 101. A negative electrode lead electrode 105 has a function of collecting the electric current generated on the back surface of the semiconductor substrate 101 and guiding the current to the exterior. This negative electrode lead terminal is formed by laser welding a copper foil onto the semiconductor substrate 101. An ID 106 consists of a bar code printed by an ink jet method on the back surface of the semiconductor substrate 101, and records a production management number. The production management number has information including a production lot of the semiconductor substrate and a serial number within such lot.
In the following the function of the ID 106 will be explained in more details.
For the purpose of cost reduction, as explained in the foregoing, the photovoltaic element is always produced in a large size, and the photovoltaic element having a large size is then divided by cutting according to the necessity or is used in such large size. The ID 106 is individually provided in each photovoltaic element of such large size, constituting the unit of mass production, for achieving various managements. For example there are managed the production conditions of the photovoltaic element, such as production date or production lot, the lots of the used materials and the data of result of performance inspection.
The performance inspection for the photovoltaic element is generally executed in a final step of production in the mass producing apparatus and prior to the division by cutting. It is executed prior to the division by cutting because a performance inspection apparatus adaptable to the element of various sizes after the cutting is expensive and requires adjustments such as a change in the position of the probe contacts and a change in the measuring positions for each change of the size, thus leading to deterioration in productivity and an increase in the cost. Therefore, the good/bad judgment in the performance inspection step is executed in the unit of the photovoltaic element prior to the division by cutting, and the result of the performance inspection is stored and managed in one-to-one correspondence with the ID specific to the photovoltaic element prior to the division by cutting. Consequently, the four IDs shown in FIG. 1D are all the same and the data reading is executed on one of such four IDs.
At least one ID is provided on each area corresponding to the photovoltaic elements after division, in order to enable investigation of the production condition etc. of each photovoltaic element after division, even in case it is divided by cutting. In the example shown in FIGS. 1A to 1D, there are provided four IDs in consideration of cases where the photovoltaic element is divided along the line 1B—1B, along the line 1C—1C, or along the lines 1B—1B and 1C—1C of FIG. 1A. The Ids of the plurality of photovoltaic elements obtained by division are mutually all the same.
Also in the example shown in FIGS. 1A to 1D, the four IDs are printed with two ink jet printers, in order to obtain low-cost IDs within the tact time. The IDs positioned along the direction of the line 1C—1C in FIG. 1A, which is the conveying direction of the article to be processed (work) in the mass production apparatus, are printed by a same ink jet printer. Also, since the IDs are printed with two ink jet printers while the work is conveyed by a conveyor, the IDs are printed in positions parallel to the direction 1C—1C in FIG. 1A. Further, the four IDs are printed in symmetric positions in the vertical and lateral directions, in order that the bar code reader can achieve reading regardless of the placing direction of the work.
However, the article to be processed (for example, photovoltaic element) having ID as shown in FIGS. 1A to 1D has caused the following problems.
One of the causes of the performance defect in the photovoltaic element is the short circuit of the element, and the element often is scarred in the short circuit portion. Also a minor scar is sometimes found even in the photovoltaic element not causing short circuit, and may detrimentally affect the reliability of the element.
Such scar is estimated to be induced by a certain interference in the mass production apparatus, and to be generated in a specified position within the mass production apparatus, based on the position of such scar in the photovoltaic element. Thus the short circuit, which is one of the cases of the performance failure of the photovoltaic element, is significantly correlated with the processing position in the mass production apparatus or with the direction of the article to be processed at processing.
However, when the photovoltaic element is symmetrical in shape, it is not possible, after the production, to identify the direction of processing (such as formation of a semiconductor layer) of the photovoltaic element in the mass production apparatus. Also the ID contains the information on the production lot or on the production date, but does not contain the information on the processing position or direction in the mass production apparatus. For this reason, in trying to specify the step or cause of scar formation in the mass production apparatus, the identification of position of cause in the mass production apparatus is difficult and requires a long time. It is therefore not possible to achieve a feedback to the maintenance service of the mass production apparatus, thereby resulting in reduction of the production yield and a cost increase due to interruption of production.
Such problem becomes more serious in case the article to be processed is divided by cutting. For example, in case the photovoltaic element shown in FIGS. 1A to 1D is divided by cutting along the line 1B—1B or 1C—1C, the elements after cutting have the same shape. Also in case the photovoltaic element is divided into four by cutting along the lines 1B—1B and 1C—1C, the pieces after cutting can be classified into two types of shape, but each type contains two pieces. Therefore, if the element is scarred in the mass production apparatus and the scarred photovoltaic elements corresponding to the scar-causing position of the apparatus have to be selected out and discarded, it is not easy to select such elements. Consequently there may cause a situation where all the elements to be subjected to such selection have to be discarded, thereby resulting in significant reduction of the production yield and increase in the cost.
In order to avoid such problems, it is conceivable to add the information on the position or direction of processing to the ID, in addition to the production lot and production condition, or to add another ID including only the position information at processing, in addition to the aforementioned ID.
However, the ID already contains information on the production lot, production apparatus and serial number, and the number of digits, for example, of the bar code has to be increased in order to add the information on position and direction of processing. The number of digits in the ordinary bar code is however limited, and an increase in the number of digits complicates the ID and increases the reading errors, so that a high-performance bar code printing system of expensive specifications must be employed in order to accommodate the increase of the number of digits. Also in case of forming an additional ID for the information on position and direction of processing, there is similarly required a new bar code printing system, and the bar code reader has also to be prepared newly. Also for accommodating the increase in the number of digits of the bar code, it is required to change the software of the ID management system and the measuring program of the performance inspection step. In either case, the management system becomes significantly complex and the increase in cost is unavoidable.
On the other hand, the information on the position or direction of the article to be processed at processing is not necessary when the production is stable without trouble, and such information will become useless when the production condition becomes stable in the future. It is considered that inclusion of such information in the ID causes a mere complication of the system with an increase in the cost.